There is no mention of HTMLOptionElement text setter to throw [1].

This patch also changes behavior to match the spec regarding using
textContent when setting internally and adds a test for this:
"On setting, the text attribute must act as if the textContent IDL
attribute on the element had been set to the new value."

[1] https://html.spec.whatwg.org/#dom-option-text

Change-Id: I5b84b33c8ed3640be95fd65afc81bbd5b9c9607c
Reviewed-on: https://chromium-review.googlesource.com/721610
Commit-Queue: Rob Buis <[email protected]>
Reviewed-by: Philip Jägenstedt <[email protected]>
Cr-Commit-Position: refs/heads/master@{#516692}